Adhesive cover seal for hermetically-sealed data storage device

ABSTRACT

A data storage device involves a plurality of continuous sidewalls and corner portions of a tub cover overlapping with and hermetically sealed with a corresponding plurality of sidewalls and corners of an enclosure base using an epoxy adhesive. Base protrusions and/or cover dimples may be used to set a suitable gap between the parts. A robust hermetic seal provides for filling the HDD with a lighter-than-air gas. A tub cover may include pleated corners, and a base may include corners having a constant-radius outer surface and sidewalls having a sloped upper surface, whereby an assembly interference fit between the base and the tub cover is formed by forcing outward each sidewall of the tub cover while forcing inward at least a portion of each corner of the tub cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of priorityto U.S. patent application Ser. No. 15/168,895 filed on May 31, 2016,which claims the benefit of priority to U.S. Provisional PatentApplication No. 62/207,888 filed on Aug. 20, 2015, the entire content ofall of which is incorporated by reference for all purposes as if fullyset forth herein.

FIELD OF EMBODIMENTS

Embodiments of the invention may relate generally to data storagedevices and more particularly to use of an adhesive cover seal forhermetically sealing a data storage device.

BACKGROUND

A hard-disk drive (HDD) is a non-volatile storage device that is housedin a protective enclosure and stores digitally encoded data on one ormore circular disks having magnetic surfaces. When an HDD is inoperation, each magnetic-recording disk is rapidly rotated by a spindlesystem. Data is read from and written to a magnetic-recording disk usinga read-write head that is positioned over a specific location of a diskby an actuator. A read-write head uses a magnetic field to read datafrom and write data to the surface of a magnetic-recording disk. A writehead makes use of the electricity flowing through a coil, which producesa magnetic field. Electrical pulses are sent to the write head, withdifferent patterns of positive and negative currents. The current in thecoil of the write head induces a magnetic field across the gap betweenthe head and the magnetic disk, which in turn magnetizes a small area onthe recording medium.

HDDs are being manufactured which are hermetically sealed with heliuminside.

Further, other gases that are lighter than air have been contemplatedfor use as a replacement for air in sealed HDDs. There are variousbenefits to sealing and operating an HDD in helium ambient, for example,because the density of helium is one-seventh that of air. Hence,operating an HDD in helium reduces the drag force acting on the spinningdisk stack and the mechanical power used by the disk spindle motor.Further, operating in helium reduces the flutter of the disks and thesuspension, allowing for disks to be placed closer together andincreasing the areal density (a measure of the quantity of informationbits that can be stored on a given area of disk surface) by enabling asmaller, narrower data track pitch. The lower shear forces and moreefficient thermal conduction of helium also mean the HDD will run coolerand will emit less acoustic noise. The reliability of the HDD is alsoincreased due to low humidity, less sensitivity to altitude and externalpressure variations, and the relative absence of corrosive gases orcontaminants.

Electronic systems that require a hermetically-sealed internal volume(e.g., a lighter-than-air gas-filled, sealed HDD) need a way ofpreventing the occurrence of leakage through the interface between thecover and the corresponding enclosure base to which the cover iscoupled. One approach is to utilize two covers: (1) one (a “firstcover”) being the typical HDD cover coupled to the base with fastenersand with a gasket seal therebetween, but not hermetically-sealed, with(2) another cover (a “second cover”) being welded to the base over thefirst cover, such as by laser welding. However, sealing approachesinvolving laser welding secondary covers to the base are a relativelycostly process in the context of the mass production of HDDs, withstrict surface finish requirements and the cost of the welding equipmentbeing main contributors to the cost. Furthermore, the welded seam isoften a weak point, which may be damaged in the field by rough handlingof the devices, whereby consequent leaks may result in an increaseddrive failure rate as compared to non-sealed products. Based at least onthe foregoing, challenges remain with welded covers forhermetically-sealed HDDs.

Any approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a plan view illustrating a hard disk drive (HDD), according toan embodiment;

FIG. 2 is an exploded view illustrating a hermetically-sealed HDD coverover-wrap approach, according to an embodiment;

FIG. 3A is an exploded view and FIG. 3B is a perspective viewillustrating a hermetically-sealed HDD gap control approach, accordingto an embodiment;

FIG. 4 is a perspective view illustrating a hermetically-sealed HDDepoxy coverage inspection approach, according to an embodiment;

FIG. 5A is an exploded view illustrating a first example HDD adhesiveseal configuration and FIG. 5B is a perspective view illustrating anassembled HDD from FIG. 5A, according to an embodiment;

FIG. 6A is a perspective view illustrating a tub cover and FIG. 6B is aperspective view illustrating a base, corresponding to a second exampleHDD adhesive seal configuration, and FIG. 6C is a perspective viewillustrating the assembled HDD using the components of 6A and 6B,according to an embodiment;

FIG. 7A is a top perspective view and FIG. 7B is a bottom perspectiveview illustrating the adhesive filling features of FIG. 6B, according toan embodiment;

FIG. 8 is a perspective view illustrating a process of injecting epoxyadhesive into the adhesive filling features of FIG. 6B, according to anembodiment;

FIG. 9A is a perspective view illustrating a cover and FIG. 9B is aperspective view illustrating a base, corresponding to a third exampleHDD adhesive seal configuration, according to an embodiment;

FIGS. 10A, 10B, and 10C are side views illustrating a cover installationprocess corresponding to the third example HDD adhesive sealconfiguration of FIGS. 9A, 9B, according to an embodiment;

FIG. 11 is a flowchart illustrating a method for assembling a datastorage device, according to a first embodiment;

FIG. 12 is a flowchart illustrating a method for assembling a datastorage device, according to a second embodiment;

FIG. 13A is an exploded view illustrating a fourth example HDD adhesiveseal configuration, FIG. 13B is a perspective view illustrating a stepin the process corresponding with the fourth example, and FIG. 13C is aperspective view illustrating an assembled HDD from the processcorresponding with the fourth example, according to an embodiment;

FIG. 14A is a perspective view illustrating a tub cover gathered corner,according to a first embodiment, and FIG. 14B is a perspective viewillustrating a tub cover tapered radius corner, according to a secondembodiment;

FIG. 15 is a bottom perspective view illustrating a tub cover havingtapered radius corners, according to an embodiment;

FIG. 16A is a top perspective view illustrating an HDD base, FIG. 16B isa cross-sectional perspective view illustrating the base of 16A, andFIG. 16C is a cross-sectional view illustrating a sidewall of the baseof 16A, according to an embodiment;

FIG. 17A is a top perspective view illustrating an HDD assembly having atub cover assembled to a base, FIG. 17B is a cross-sectional side viewillustrating mating sidewalls of the assembly of 17A, and FIG. 17C is across-sectional side view illustrating a corner area of the assembly of17A, illustrating a portion of an assembly process, according to anembodiment;

FIG. 18 is a flow diagram illustrating a method of assembling a datastorage device, according to an embodiment; and

FIG. 19 is a flow diagram illustrating a method of assembling a datastorage device, according to an embodiment.

DETAILED DESCRIPTION

Approaches to an adhesive seal for a hermetically-sealed data storagedevice are described. In the following description, for the purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the embodiments of the invention describedherein. It will be apparent, however, that the embodiments of theinvention described herein may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order to avoid unnecessarily obscuring theembodiments of the invention described herein.

Physical Description of an Illustrative Operating Context

Embodiments may be used in the context of a hermetic seal for a harddisk drive (HDD) storage device. Thus, in accordance with an embodiment,a plan view illustrating an HDD 100 is shown in FIG. 1 to illustrate anexemplary operating context.

FIG. 1 illustrates the functional arrangement of components of the HDD100 including a slider 110 b that includes a magnetic read-write head110 a. Collectively, slider 110 b and head 110 a may be referred to as ahead slider. The HDD 100 includes at least one head gimbal assembly(HGA) 110 including the head slider, a lead suspension 110 c attached tothe head slider typically via a flexure, and a load beam 110 d attachedto the lead suspension 110 c. The HDD 100 also includes at least onerecording medium 120 rotatably mounted on a spindle 124 and a drivemotor (not visible) attached to the spindle 124 for rotating the medium120. The read-write head 110 a, which may also be referred to as atransducer, includes a write element and a read element for respectivelywriting and reading information stored on the medium 120 of the HDD 100.The medium 120 or a plurality of disk media may be affixed to thespindle 124 with a disk clamp 128.

The HDD 100 further includes an arm 132 attached to the HGA 110, acarriage 134, a voice-coil motor (VCM) that includes an armature 136including a voice coil 140 attached to the carriage 134 and a stator 144including a voice-coil magnet (not visible). The armature 136 of the VCMis attached to the carriage 134 and is configured to move the arm 132and the HGA 110 to access portions of the medium 120, all collectivelymounted on a pivot shaft 148 with an interposed pivot bearing assembly152. In the case of an HDD having multiple disks, the carriage 134 maybe referred to as an “E-block,” or comb, because the carriage isarranged to carry a ganged array of arms that gives it the appearance ofa comb.

An assembly comprising a head gimbal assembly (e.g., HGA 110) includinga flexure to which the head slider is coupled, an actuator arm (e.g.,arm 132) and/or load beam to which the flexure is coupled, and anactuator (e.g., the VCM) to which the actuator arm is coupled, may becollectively referred to as a head stack assembly (HSA). An HSA may,however, include more or fewer components than those described. Forexample, an HSA may refer to an assembly that further includeselectrical interconnection components. Generally, an HSA is the assemblyconfigured to move the head slider to access portions of the medium 120for read and write operations.

With further reference to FIG. 1, electrical signals (e.g., current tothe voice coil 140 of the VCM) comprising a write signal to and a readsignal from the head 110 a, are transmitted by a flexible cable assembly(FCA) 156 (or “flex cable”). Interconnection between the flex cable 156and the head 110 a may include an arm-electronics (AE) module 160, whichmay have an on-board pre-amplifier for the read signal, as well as otherread-channel and write-channel electronic components. The AE module 160may be attached to the carriage 134 as shown. The flex cable 156 may becoupled to an electrical-connector block 164, which provides electricalcommunication, in some configurations, through an electricalfeed-through provided by an HDD housing 168. The HDD housing 168 (or“enclosure base” or simply “base”), in conjunction with an HDD cover,provides a semi-sealed (or hermetically sealed, in some configurations)protective enclosure for the information storage components of the HDD100.

Other electronic components, including a disk controller and servoelectronics including a digital-signal processor (DSP), provideelectrical signals to the drive motor, the voice coil 140 of the VCM andthe head 110 a of the HGA 110. The electrical signal provided to thedrive motor enables the drive motor to spin providing a torque to thespindle 124 which is in turn transmitted to the medium 120 that isaffixed to the spindle 124. As a result, the medium 120 spins in adirection 172. The spinning medium 120 creates a cushion of air thatacts as an air-bearing on which the air-bearing surface (ABS) of theslider 110 b rides so that the slider 110 b flies above the surface ofthe medium 120 without making contact with a thin magnetic-recordinglayer in which information is recorded. Similarly in an HDD in which alighter-than-air gas is utilized, such as helium for a non-limitingexample, the spinning medium 120 creates a cushion of gas that acts as agas or fluid bearing on which the slider 110 b rides.

The electrical signal provided to the voice coil 140 of the VCM enablesthe head 110 a of the HGA 110 to access a track 176 on which informationis recorded. Thus, the armature 136 of the VCM swings through an arc180, which enables the head 110 a of the HGA 110 to access varioustracks on the medium 120. Information is stored on the medium 120 in aplurality of radially nested tracks arranged in sectors on the medium120, such as sector 184. Correspondingly, each track is composed of aplurality of sectored track portions (or “track sector”) such assectored track portion 188. Each sectored track portion 188 may includerecorded information, and a header containing error correction codeinformation and a servo-burst-signal pattern, such as anABCD-servo-burst-signal pattern, which is information that identifiesthe track 176. In accessing the track 176, the read element of the head110 a of the HGA 110 reads the servo-burst-signal pattern, whichprovides a position-error-signal (PES) to the servo electronics, whichcontrols the electrical signal provided to the voice coil 140 of theVCM, thereby enabling the head 110 a to follow the track 176. Uponfinding the track 176 and identifying a particular sectored trackportion 188, the head 110 a either reads information from the track 176or writes information to the track 176 depending on instructionsreceived by the disk controller from an external agent, for example, amicroprocessor of a computer system.

An HDD's electronic architecture comprises numerous electroniccomponents for performing their respective functions for operation of anHDD, such as a hard disk controller (“HDC”), an interface controller, anarm electronics module, a data channel, a motor driver, a servoprocessor, buffer memory, etc. Two or more of such components may becombined on a single integrated circuit board referred to as a “systemon a chip” (“SOC”). Several, if not all, of such electronic componentsare typically arranged on a printed circuit board that is coupled to thebottom side of an HDD, such as to HDD housing 168.

References herein to a hard disk drive, such as HDD 100 illustrated anddescribed in reference to FIG. 1, may encompass an information storagedevice that is at times referred to as a “hybrid drive”. A hybrid driverefers generally to a storage device having functionality of both atraditional HDD (see, e.g., HDD 100) combined with solid-state storagedevice (SSD) using non-volatile memory, such as flash or othersolid-state (e.g., integrated circuits) memory, which is electricallyerasable and programmable. As operation, management and control of thedifferent types of storage media typically differ, the solid-stateportion of a hybrid drive may include its own corresponding controllerfunctionality, which may be integrated into a single controller alongwith the HDD functionality. A hybrid drive may be architected andconfigured to operate and to utilize the solid-state portion in a numberof ways, such as, for non-limiting examples, by using the solid-statememory as cache memory, for storing frequently-accessed data, forstoring I/O intensive data, and the like. Further, a hybrid drive may bearchitected and configured essentially as two storage devices in asingle enclosure, i.e., a traditional HDD and an SSD, with either one ormultiple interfaces for host connection.

Introduction

The term “hermetic” will be understood to describe a sealing arrangementdesigned to have nominally no (or negligible) gaseous leakage orpermeation paths. While terms such as “hermetic”, “negligible leakage”,“no leakage”, etc. may be used herein, note that such a system wouldoften still have a certain amount of permeability and, therefore, not beabsolutely leak-free. Hence, the concept of a desired or target “leakrate” may be used herein.

The term “substantially” will be understood to describe a feature thatis largely or nearly structured, configured, dimensioned, etc., but withwhich manufacturing tolerances and the like may in practice result in asituation in which the structure, configuration, dimension, etc. is notalways or necessarily precisely as stated. For example, describing asidewall as “substantially vertical” would assign that term its plainmeaning, such that the sidewall is vertical for all practical purposesbut may not be precisely at 90 degrees.

Recall that electronic systems that require a hermetically-sealedinternal volume (e.g., a lighter-than-air gas-filled, sealed HDD) need away of preventing the occurrence of leakage through the cover-to-baseinterface, with one approach being to utilize two covers, the second ofwhich may be laser welded to the base, over the first cover.

Consider for example that a 3.5″ form factor HDD has an enclosureperimeter approximately 500 mm long. If a simple flat metal cover isattached to the tops of the vertical sidewalls of a tub-style base, thewidth of the joint might typically be around 1 mm, or perhaps 2 mm atmost. The sidewalls of the base are typically 5 mm thick or less, toprovide room for internal components. In particular, the regions wherethe sidewalls pass by the outer diameter (OD) of the disk stack must beespecially thin (at most 3 mm thick) simply because of the size of thedisks (e.g., 95 mm diameter), the width of the form factor (101.6 mm)and provisioning for minimal clearance between the base sidewalls andthe rotating disks. Furthermore, the full width of a sidewall generallycannot be used to create a sealing face for the cover. The assemblyprocess for sealed drives may involve first attaching an inner coverwith a preliminary gasket seal, followed by servo-writing andmanufacturing test (which has imperfect yield, so performing these whilethe second cover is not in place allows reworkability), followed byattaching a hermetically-sealed second cover (after second coverattachment, the drive is no longer reworkable because the second coverseal/attachment is not reversible). Because the preliminary gasket sealof the first cover generally requires some sidewall top face width toachieve a seal, the amount of remaining sidewall top face width isreduced to around only 1 mm or less at the narrowest points next to theouter diameter of the disks.

While laser welding of the second cover to the base can successfullycreate a permanent hermetic seal with very little top face width on thebase sidewall, laser welding is a relatively expensive process. A lowercost approach than laser welding, for joining and sealing thecover-to-base interface, may be to use an epoxy adhesive. Adhesivesealing methods described herein can serve as less expensive and aphysically more robust alternatives to laser welding, and may contributeto achieving epoxy seals that meet the leak and form-factor requirementswhile being suitable for cost-effective mass manufacturing.

Adhesive Seal for Hermetically-Sealed Data Storage Device-Generally

An adhesive seal uses an adhesive material, such as an epoxy or apressure sensitive adhesive (PSA), to fill gaps between two parts. Forexample, an adhesive seal may be used to fill gaps between a secondcover and a base casting of an HDD, which are individually largelyimpermeable to helium, to create a seal between the two parts that meetsa certain leak requirement.

Achieving a low enough leak rate for a cover seal using epoxy generallymay or should consider the following: (a) the type of epoxy adhesiveused, for a non-limiting example, a low permeability epoxy adhesive suchas alumina-filled H72 epoxy from Epoxy Technology (EpoTek) is consideredsuitable; (b) the bond line thickness between the cover and the base,with a preference for a thin bond line, for a non-limiting example,around 0.1 mm or less is considered suitable; and (c) the width (orheight) of the seal, which is the overlap region between the cover andthe base, with a preference for a wide (or long) seal, for anon-limiting example, around 5-10 mm or more is considered suitable.

The need for a wide seal [e.g., (c) above] presents a challenge toachieving an adequate seal with a simple horizontal bond line between abase sidewall and a cover. Although reducing the width of the bond couldbe compensated for by reducing the thickness of the bond, consistentlyachieving such a thin bond line would rely on, for example, anexceptionally good surface finish (e.g., low roughness) and extremelytight geometric tolerances (e.g., planarity, or flatness) on the matingsurfaces and/or very small or no filler particles within the epoxy(which, by the way, are useful for achieving low permeability of theepoxy in the first place). However, achieving a bond line having athickness of approximately 0.05-0.1 mm is considered achievable withtypical machined surfaces and commercially available epoxy.

Cover Over-Wrap Approach

A hermetically-sealed HDD (or, throughout this description, other typesof data storage devices) enclosure may comprise a base and one or morecovers, recalling that one approach is to employ a conventional firstcover with a second cover affixed (e.g., welded) thereover. Hereinthroughout, unless otherwise indicated the term “cover” is used to referto the second cover. The base is typically thicker than the cover andhas more features for component attachments and customer mounts. Thecover is simpler and mostly used for creating a closed,hermetically-sealed enclosure.

A quality laser weld has almost no permeability to helium, thus a thinlaser weld can satisfy the typical leak requirement. However, adhesivesare relatively more permeable, and require a longer seal. To enable alonger seal within the common drive form factor, a more complex coverdesign may be beneficial. As mentioned, near the disk OD, the top edgeof the base wall is narrow and, as a result, a long seal can only becreated between the cover and the vertical sidewalls of the base.

FIG. 2 is an exploded view illustrating a hermetically-sealed hard diskdrive (HDD) cover over-wrap approach, according to an embodiment. Forsake of simplicity and clarity, FIG. 2 only depicts an HDD base 202 andan HDD cover 204 of an HDD enclosure 200, omitting the illustration ofany HDD internal components and a first cover, while illustrating anexample internal shape of the base 202 to depict certain features suchas horizontal surfaces 202 b. Reference is made to FIG. 1 for adescription of other components of a hard disk drive that may beimplemented in or with the HDD enclosure 200. The manner in which thecover 204 may be configured and fabricated may vary from implementationto implementation, according to various embodiments described elsewhereherein. Regardless, with a “cover over-wrap” approach, according to anembodiment, the hermetic seal (or simply “seal”) is fabricated onto thevertical sidewalls 202 a of the base 202 (“wall seal” portion) and ontothe horizontal surfaces 202 b in the corners of the base 202(“horizontal seal” portion), whereby the horizontal seal in the cornerconnects the seal corresponding to the discontinuous sides 204 a of thecover 204, and whereby the horizontal seal is between the planar topportion 204 b of cover 204 and each corresponding horizontal surface 202b of base 202.

According to an embodiment, the cover 204 is fabricated by bending ametallic sheet. Related embodiments include (a) pre-forming the cover204, by bending a metallic sheet prior to assembly with the base 202,and (b) forming a “shape-in-place” cover 204, by bending a metallicsheet while assembling with the base 202, thereby effectively utilizingthe base 202 as a shaping mold.

According to an alternative embodiment, the cover may be pre-formed intoa bath tub-shaped (or simply “tub”) cover, which is pre-formed into a3-dimensional shape having the main planar portion and the continuoussidewalls prior to assembly with the base. A tub cover is described inmore detail elsewhere herein, such as with reference to FIGS. 6A-C, 9A,9B, 10A-C. For a non-limiting example, a pre-formed tub cover may befabricated using a deep drawing process, which is a well-known sheetmetal forming process, thereby forming a deep-drawn tub cover. Adeep-drawn tub cover would have no discontinuity in the corners, but maybe more challenging to use with solid adhesive films (e.g.,pressure-sensitive adhesive, or “PSA” films) that benefit from fullcontact with the other mating part.

Sealing Adhesive Materials and Applications

As a variety of adhesives exist, one fundamental characteristic toconsider in selecting a suitable adhesive for forming a hermetic sealbetween or among a cover 204 and base 202 in a helium-filled HDD is forthe adhesive to have a low permeability to helium. Likewise, if someother lighter-than-air gas is used for filling an HDD, the adhesive'spermeability to that gas would be a characteristic to consider.

With a proper joint design, epoxies have a sufficient permeability tohelium to create an effective helium seal. Epoxies can be applied inliquid form, or as a tacky film pre-applied or slathered onto a part(i.e., “B-staged”). In the liquid form, the epoxy can be applied to apart before the parts are assembled together if a high viscosityformulation is used. Alternatively, a low viscosity liquid epoxy can bedispensed and drawn into the seal using capillary action (or “capillaryflow”), referring to the tendency of a liquid to flow or be drawn intonarrow spaces without the assistance of external forces, i.e., as aresult of the intermolecular attraction within and between the liquidand solid materials. While other adhesives, such as PSAs, generally havea higher permeability than epoxies, at least one type (Adhesive ResearchPSA EL-92734) can still meet the application requirements. Suchadhesives can be applied prior to mating the parts. These adhesivegenerally do not require a curing step after joining of the matingparts, and are preferred in that sense.

For embodiments in which a liquid epoxy seal is used, the flow of theepoxy should preferably be managed. According to an embodiment, onetechnique for controlling the liquid epoxy flow is to have a limitednumber of fill points, where a sufficient amount of epoxy is injected ordispensed and is then transferred into the joint by capillary action.According to a related embodiment, one or more channels connected to oneor more fill points are provided, which help spread the epoxy along theseal periphery, thereby shortening the capillary flow length. Suchchannels may be formed constituent to the cover 204 (FIG. 2) and/or thebase 202 (FIG. 2), or may be formed by a secondary part such as adhesivetape, for non-limiting examples. According to another embodiment, theepoxy may be applied (e.g., dispensed) along the whole perimeter of thebase-cover interface, in which case a channel can be used to contain thedeposited epoxy until it is drawn into the joint using capillary action.

For embodiments in which a PSA seal is used, the HDD assembly maycomprise a shape-in-place sheet metal cover (e.g., cover 204 of FIG. 2)and a base (e.g., base 202 of FIG. 2), according to an embodiment. Thecover 204 or the base 202 has the PSA pre-applied as a backing. First,the blank sheet metal composing the cover 204 is aligned to the base202. Next, the sheet metal is brought into contact and pressed againstthe base 202 to create the seal in the flat top areas of the base 202,including the corners. Finally, the sheet metal is bent so thatsidewalls 204 a of the cover 204 are formed and pressed onto thesidewalls 202 a of the base 202 to create the seal on the matingsidewalls, by way of the PSA. The assembly process should be performedsuch that the cover 204 fully conforms and bonds to the base 202,leaving no to negligible void channels for leaking helium or some otherlighter-than-air gas. A thin and/or soft cover and/or a proper bendingprocedure, such as with a rolling action, may be used to ensure properassembly and sealing.

According to an embodiment, a hybrid of the foregoing embodiments may beimplemented. For example, a PSA may be used to fixture and/or set a gapbetween a base (e.g., base 202 of FIG. 2) and a cover (e.g., cover 204of FIG. 2), with epoxy then used to complete the sealing arrangementand, hence, to obtain a low-leak-rate seal.

Seal Configurations

Generally, the path of an adhesive seal can take multiple forms. Forexample, an epoxy seal between a tub cover and a base may follow asimple path around the perimeter of the sidewalls of the base and thetub cover. In such an adhesive seal configuration, it is preferable thatthe tub cover has a complete tub shape (i.e., having continuoussidewalls, including corners) and a suitable seal all the way around theperimeter, including the corners. For another example and with referenceto FIG. 2, which may apply to both a tub cover and/or a bent sheet metalcover, the seal 206 (FIG. 2) may be formed along the sidewalls of thebase and cover for the long straight parts of the sidewalls (denoted as“wall seal” in FIG. 2), and then be formed up over the top in thecorners (denoted as “horizontal seal” in FIG. 2). In the corners, theseal 206 is between corner surfaces 202 b on the base 202 and the planartop portion 204 b of the cover 204. This more complex path allows forcovers with open corners (e.g., bent/folded sheet metal covers, such as204), or tub covers which do not seal well in the corners. Thehorizontal corner surfaces 202 b of the base 202 should be wide enoughso that a seal width of at least several millimeters wide (preferablyaround 10 mm wide, according to an embodiment) can be achieved, as it isalong the sidewalls (e.g., sidewalls 202 a of base 202).

One approach to assembling and sealing a cover onto a base is to use aninterference fit, whereby the cover 204 sidewalls 204 a are deflectedoutward, thus exerting inward force to the base 202 sidewalls 202 awhile pushing the cover 204 down onto the base 202. However, a simpleinterference fit can risk tearing or cracking the cover 204 material,especially with a tub cover. Such risk is due, at least in part, tolimitations on the manufacturing tolerances associated with both thecover 204 and the base 202. Thus, the precise amount of interference andthe corresponding amount of stretching and cover perimeter increase maycause sufficient stress on the cover 204 to introduce risk of tearing orcracking the cover 204.

Seal Thickness Control

With a permeable material, naturally the leak rate increases with theseal thickness because a thicker seal provides a wider leak channel.Therefore, in practice there is a maximum limit on the seal thicknessthat would correspond with a given allowable leak rate for the seal.Furthermore, the thickness of the adhesive seal should be controlled inview of the mating part tolerances. A suitable epoxy adhesive seal widthin on the order of around 0.1 mm, for a non-limiting example.

With continuing reference to FIG. 2, one approach to controlling the gapbetween a base, such as base 202, and a cover, such as cover 204, is touse protrusions or ridges on the base surface, according to anembodiment. FIG. 3A is an exploded view and FIG. 3B is a perspectiveview illustrating a hermetically-sealed hard disk drive (HDD) gapcontrol approach, according to an embodiment. For sake of simplicity andclarity, FIG. 3A only depicts an HDD base 302 and an HDD cover 304 of anHDD enclosure 300, omitting the illustration of any HDD internalcomponents and a first cover. Reference is made to FIG. 1 for adescription of other components of a hard disk drive which may beimplemented in or with the HDD enclosure 300.

As depicted in FIGS. 3A and 3B, the base 302 of enclosure 300 comprisesa plurality of protrusions 306, protruding from and spaced around theouter surface of the sidewalls 302 a of the base 302. These protrusions306 may be cast with or machined into the base 302, for example. Thenumber, shape and spacing of the protrusions 306 depicted in FIGS. 3A,3B are each depicted for purposes of example. Hence, the number, shapeand spacing of the protrusions 306 may vary from implementation toimplementation based, for non-limiting examples, on the respectivegeometries of the base 302 and cover 304, the type of adhesive used andits viscosity and permeability, the desired leak rate through the sealfor the particular gas used, and the like.

According to an alternative embodiment, dimples 308 may be formed ontothe cover 304 in order to set the gap between the base 302 and the cover304. For example, an array of dimples 308 (e.g., with a height ofapproximately 0.05-0.1 mm) may be formed into the cover 304 sidewalls304 a (thereby creating a form of controlled roughness) to set the gapwidth but to allow a suitable flow of epoxy throughout the seal area.While, for purposes of simplicity and clarity, dimples 308 are depictedon only one sidewall 304 a of the cover 304, the dimples 308 may beimplemented on each sidewall 304 a. Furthermore, a combination ofprotrusions 306 on the base 302 and dimples 308 on the cover 304,possibly in an alternating pattern, may be used to set the desired gapbetween the base 302 and the cover 304, whereby such a configurationcould contribute to a more desirable leak path, for example.

According to an embodiment, the sidewalls 304 a of the cover 304 arebent in past vertical, such that the sidewalls 304 a are preloadedagainst the base 302 as the cover 304 is assembled onto the base 302.

Whereas the protrusions 306 or dimples 308 set the gap between therespective sidewalls 304 a of the cover 304 and the sidewalls 302 a ofthe base 302 at the perimeter edge 311 of the sidewalls 304 a, a bend310 at the edge 311 of the cover 304 may be used to add rigidity to thesidewall 304 a, according to an embodiment. With a cover 304configuration in which a bend 310 is implemented, a fewer number ofprotrusions 306 may be used to set the desired uniform gap along thewhole edge 311. The bend 310 at the edge 311 can also serve as a chamferto guide the insertion of an over-bent cover 304 onto the base 302. Thebend 310 can be pressed to flat or machined off at the end of theassembly process, if desired.

According to an embodiment, an alternative method for setting the gapbetween a base (e.g., base 202 of FIG. 2) and a cover (e.g., cover 204of FIG. 2) is to use adhesive ridges (or “steps”) pre-applied to eitherthe base 202 or the cover 204. In this scenario, the cover shouldpreferably be bent to an open position (i.e., with the sidewalls 204a>90° from the planar top portion 204 b), such that the cover 204 can beplaced over the base 202 and rest on the top surfaces of the base 202without the sidewalls 204 a of the cover 204 making contact with thesidewalls 202 a of the base 202. Once the cover 204 is fully establishedor seated onto the base 202, the sidewalls 204 a are to be pressed tocontact and bond onto the base 202 by way of the adhesive steps (notvisible). Thus, the thickness of the adhesive steps sets the gap betweenthe base 202 and the cover 204, however, the steps are not expected tocreate a seal. Rather, the steps are primarily used to control the gapin the presence of any spring-back loads or tolerance mismatch. Once thecover 204 is fully seated onto the base 202 and the sidewalls 204 apressed into contact with the sidewalls 202 a of the base 202,additional adhesive may be applied to create a complete seal.

If setting a gap as close as possible is desired, the cover 204 can bebent and formed onto the base 202 directly (i.e., a shape-in-placecover), according to an embodiment. To minimize the amount the sidewalls204 a may spring back after formation, a thicker sheet and/or a softermaterial for the cover 204 may be considered for use. If theshape-in-place forming process forces are too significant for the base202 to handle, then a mostly pre-formed cover 204 can be pressed ontothe base 202 to take the exact shape of the base, with minimalapplication of force(s) to the base 202. According to an embodiment, analternative way of setting a close gap would be to use a pre-formedcover 204 that has been pre-stressed and shaped, such that itsinterference and spring-action results in the cover 204 conforming ontothe sidewalls 202 a of the base 202.

With an interference fit with a tub cover, the cover 204 sidewalls 204 aare deflected outward, thus exerting inward force to the base 202sidewalls 202 a while pushing the cover 204 down onto the base 202.However, a simple interference fit can risk tearing or cracking thecover 204 material. Such risk is due, at least in part, to limitationson the manufacturing tolerances associated with both the cover 204 andthe base 202. Thus, the precise amount of interference and thecorresponding amount of stretching of the tub cover perimeter may fallwithin a range that introduces risk of tearing or cracking the cover204.

Fixturing

When bonding the base 202 (FIG. 2) and cover 204 (FIG. 2) together, themating parts should be positioned accordingly and held together for theadhesive to bond, a process referred to as “fixturing”. Fasteners, suchas screws and rivets, can be used to hold the mating parts. Any holesassociated with such fasteners are preferably outside of the seal areaor, if inside the seal area, any gaps between the fasteners andcorresponding holes are filled with sealing adhesive. Alternatively, theinitial tackiness of an adhesive is one way to hold the mating partstogether, which can work reasonably well with PSA and B-staged epoxy.Another alternative, which is perhaps more suitable for liquid epoxies,is to use an interference fit. With an interference fit, the fittingforces can be managed and limited by relying on the flexibility of oneof the mating parts. Further, a clearance fit with controlled tolerancescan be used for fixturing. Still further, a separate externalfixture/tool may also be used.

Surface Treatments

A suitable surface treatment of one or both of the mating parts (i.e.,base 202 and cover 204 of FIG. 2) can significantly improve the adhesivebonding strength, as well as improve the aforementioned capillaryaction, which is important in scenarios in which liquid epoxy is appliedrelying on capillary flow. Several suitable surface treatmenttechniques, according to embodiments, are (a) bead-blasting (or abrasiveblasting, generally); (b) chemical etching, (c) formed features, e.g.,knurling, and (d) cut features, e.g., offset fly cutter marks.

Inspection for Epoxy Coverage

In the scenarios in which liquid epoxy is used, adequate filling of thejoint interface by epoxy is needed to provide the required sealingperformance. Although a proper design (e.g., surface treatment forenhanced capillary flow, or seal joint gap control, as describedelsewhere herein) can ensure complete epoxy flow coverage, inspectionand monitoring techniques may still be necessary for quality control andyield improvement.

FIG. 4 is a perspective view illustrating a hermetically-sealed harddisk drive epoxy coverage inspection approach, according to anembodiment. Similar to previously-described embodiments, HDD 400comprises a base 402 and a cover 404. According to an embodiment, HDD400 further comprises a plurality of inspection holes 406, which aresmall holes spaced at suitable intervals around the periphery of thecover 404. As the adhesive wicks around the perimeter of the cover-basegap, it would fill each inspection hole 406. After the adhesive iscured, if the adhesive is visible in each inspection hole 406, it ishighly likely and thus can be assumed that each path from an adhesiveintroduction point to a inspection hole 406 has been filled withadhesive. Hence, adequate adhesive coverage at the cover-base interfacecan be ensured through use of the inspection holes 406. According to arelated embodiment, a colorant is added to the adhesive for ease ofinspection. Such an inspection via the inspection holes 406 may bemanually performed by a human operator, or may be automated usingcomputer-vision systems, for example. Alternatively, an ultra-soundinspection method may be used to assess epoxy coverage between the coverand the base.

Example Hard Disk Drive Cover Adhesive Seal Configurations

The foregoing design alternatives can be combined in numerous ways toimplement a detailed hard disk drive adhesive seal design. Severalnon-limiting example embodiments, suitable for sealing a hard disk driveand combining features described elsewhere herein, are described asfollows.

Capillary Epoxy Seal with Bent Cover

FIG. 5A is an exploded view illustrating a first example HDD adhesiveseal configuration and FIG. 5B is a perspective view illustrating anassembled HDD from FIG. 5A, according to an embodiment. In thisembodiment, a pre-formed bent (or folded) sheet metal cover 504 (“bentcover 504”) is positioned over a base 502. The base 502 has protrusions506, which are 25-100 micrometers thick, for example, and are used forsetting a gap between the bent cover 504 and the base 502. Once the bentcover 504 is positioned over the base 502, the assembly is placed upsidedown, with the bent cover 504 resting against the supporting surface.Epoxy is applied at the edge of the seal, either all along the peripheryor at fixed injection points. The HDD assembly 500 is placed in an ovenfor the epoxy to cure at elevated temperatures. The dispensed epoxy isautomatically drawn into the seal using capillary action, which canmanage epoxy flow without leakage in the corners.

With a pre-formed bent cover, tight gap control can be achieved, wherethe bend-to-bend tolerances can be controlled by bending the cover ontoa master die. Any bend angle tolerance can be absorbed by theflexibility of the part, and the cover may be over-bent such that it ispreloaded on the base when assembled. While the first example HDDadhesive seal configuration shown and described in reference to FIGS.5A, 5B is in the context of a pre-formed bent cover 504, similarly, ashape-in-place type of bent cover could be used, as described elsewhereherein. With a shape-in-place type of bent cover, base castingtolerances are readily absorbed. Thus, a shape-in-place approach canpotentially avoid base machining processes.

Capillary Epoxy Seal with Tub Cover and Fixed Fill Points

FIG. 6A is a perspective view illustrating a tub cover and FIG. 6B is aperspective view illustrating a base, for a second example HDD adhesiveseal configuration, and FIG. 6C is a perspective view illustrating theassembled HDD using the components of 6A and 6B, according to anembodiment. A variation on the bent sheet cover-based seal illustratedand described in reference to FIGS. 5A, 5B, employing a differentcombination of the approaches described elsewhere herein, is the use ofa deep-drawn tub cover 604 and a number of fixed adhesive fillingfeatures 606 in a base 602 of an HDD assembly 600. For example, the tubcover 604 may comprise a 5-degree wall slope and the base 602 maycomprise a 5-degree chamfer (as opposed to a vertical wall) tofacilitate placement and positioning of the tub cover 604 onto the base602. Additionally, or alternatively, an interference fit may be utilized(e.g., with a relatively soft aluminum cover), forcing the cover overthe edge of the base to form the cover to the actual base dimensions.The filling features 606 may be defined by slots or wells into whichliquid epoxy is dispensed while the HDD assembly 600 is positionedupside down.

FIG. 7A is a top perspective view and FIG. 7B is a bottom perspectiveview illustrating the adhesive filling features of FIG. 6B, according toan embodiment. In this example, ten adhesive filling features 606 aredepicted for a non-limiting example, as slots, roughly equally spacedalong the perimeter of the base 602. Because the adhesive fillingfeatures 606 should to be located in areas where the sidewall of thebase 602 is relatively thick, the thin-walled area near the disk outerdiameter is preferably avoided.

FIG. 8 is a perspective view illustrating a process of injecting epoxyadhesive into the adhesive filling features of FIG. 6B, according to anembodiment. With the HDD assembly 600 upside down, with the tub cover604 in place over the base 602, a low viscosity liquid epoxy can besimultaneously dispensed into the ten adhesive filling features 606(using corresponding dispensers 610), as depicted in FIG. 8. Capillaryaction spreads the epoxy rapidly along the entire perimeter interfacebetween the base 602 and the tub cover 604.

As an aside, a possible advantage of a tub cover over a bent sheet metalcover is that there is considerably less possibility of epoxy leakagefrom the corners of a cover while the drive is upside down because thetub shape contains the epoxy around the entire perimeter interface.Regardless, care should still be taken to dispense an appropriate amountof epoxy into each adhesive filling feature 606 to avoid overflow. Ifeach adhesive filling feature 606 has an adequate volume to serve as asource for enough epoxy to fill the entire perimeter seal, then a singleinjection of epoxy can be performed quickly, and the capillary spreadingcan take place without further dispensing of epoxy. On the other hand,if the adhesive filling features 606 do not have enough volume toprovide for the full amount of a given epoxy (with a correspondingviscosity) needed to fill the complete seal, then multiple injectionsmay be used, or a slower-rate single injection that allows somespreading while the filling process is being performed. To cure theepoxy, the HDD assembly 600 may be placed upside down in an oven, forexample, where the weight of the HDD assembly 600 maintains the base 602and the tub cover 604 together while the epoxy solidifies and bonds theparts together.

A challenge associated with a deep-drawn tub cover, such as tub cover604, is that tight tolerances would be preferable for both the slopedchamfer on the base (if used) and the sidewalls of the tub cover (ifused), in order to achieve a small, well-controlled gap all the wayaround the perimeter for the epoxy to fill by capillary action. In sucha scenario, in lieu of or in addition to such tight tolerances,protrusions such as protrusions 306 (FIGS. 3A, 3B) may be used with thisembodiment to help set the gap spacing.

Epoxy Bead Seal With Tub Cover With Self-Alignment Skirt

While capillary filling works well for low-viscosity epoxy, adisadvantage of low-viscosity epoxy is that it tends to have higher gaspermeability in the cured state than a higher-viscosity epoxy. Ahigher-viscosity epoxy filled with solid particles may have too high aviscosity for capillary filling, but shows significantly lower gaspermeability in the cured state. Thus, a sealing approach directed at ahigh-viscosity epoxy is as follows.

FIG. 9A is a perspective view illustrating a cover and FIG. 9B is aperspective view illustrating a base, illustrating a third example HDDadhesive seal configuration, according to an embodiment. A tub cover 904(e.g., deep-drawn) is configured to mate with a base 902 havingappropriate mating surfaces, such as a chamfer 902 a-1 (e.g., a 25degree chamfer, for a non-limiting example) along the perimeter sidewall902 a. The tub cover 904 and the base 902 are intended for bondingtogether, i.e., hermetically sealing, by way of a bead 906 ofhigh-viscosity epoxy adhesive. In this context, a “bead” refers to anapplied line of adhesive. While FIG. 9A depicts an applied epoxy beadalong only one side, for purposes of simplicity and clarity, in practiceepoxy should be dispensed in a continuous bead 906 around the completeperimeter of the sidewall 904 a of the tub cover 904, or the sidewall902 a of the base 902.

According to an embodiment, the sidewall 904 a of tub cover 904 has asloped section 904 a-1, where the epoxy seal is formed, and an alignmentskirt 904 a-2, which may have a lower slope or which may be completelyvertical (as depicted in this example). The alignment skirt 904 a-2serves to self-align the cover 904 as it is lowered onto the base 902 inorder to prevent accidental smearing of the epoxy bead 906 by unwantedcontact.

FIGS. 10A-10C includes side views illustrating a cover installationprocess associated with the third example HDD adhesive sealconfiguration of FIG. 9A, 9B, according to an embodiment. Prior tolowering the cover 904 onto the base 902, the epoxy bead 906 has beenapplied as shown in FIG. 9A. FIG. 10A depicts the cover 904, with epoxybead 906, positioned over the base 902. As the cover 904 is lowered tothe point of touching the base 902, as depicted in FIG. 10B, thealignment skirt 904 a-2 makes contact with the sidewall 902 a of thebase 902 and self-aligns the cover 904 before the epoxy bead 906 cancome into contact with anything. Unwanted contact with the wrong part ofthe base 902 could smear the epoxy bead 906, thereby preventing a goodseal from forming. In FIG. 10C, the cover 904 is fully in place, and theepoxy ends up between the sloped section 904 a-1 of the cover 904 andthe chamfer 902 a-1 of the sidewall 902 a of the base 902. The beadcompresses to a thin film, filling the gap along the sloped section 904a-1 and forming a robust hermetic seal. Because a high-viscosity epoxyis used in this example scenario, a narrower seal width may be used,such as only a few millimeters wide. The width of the seal can beadjusted, however, by changing the slope of the sloped section 904 a-1and the amount of the thickness of the sidewall 902 a of the base 902consumed by the chamfer 902 a-1. After installation of the cover 904onto the base 902, the epoxy can be cured in an oven with the HDDassembly upside down, holding the cover and baseplate together until theepoxy solidifies and bonds the parts together.

Methods of Assembling a Data Storage Device with a Bent Sheet MetalCover and Perimeter Adhesive Seal

FIG. 11 is a flow diagram illustrating a method of assembling a datastorage device, according to an embodiment.

At block 1102, a first cover is attached to an enclosure base having aplurality of sidewalls. For example, a conventional HDD cover may beattached to the base with fasteners and with a gasket seal therebetween,whereby servo-writing and manufacturing test may follow.

At block 1104, each of a plurality of sidewalls extending from a topportion of a bent sheet metal cover is positioned to overlap at least inpart with a corresponding sidewall of the base. For example, eachsidewall 204 a (FIG. 2) extending from top portion 204 b (FIG. 2) of abent sheet metal version of cover 204 (FIG. 2) is positioned to overlapwith a corresponding sidewall 202 a (FIG. 2) of base 202 (FIG. 2), wherethe bent sheet metal cover 204 may be a pre-formed cover or ashape-in-place cover.

At block 1106, an epoxy adhesive is applied at an interface of eachsidewall of the bent sheet metal cover and each corresponding sidewallof the base to form a hermetic seal between (or “among” the parts, asthe adhesive could be applied at or near where the bottom edge of thecover meets the base) the bent sheet metal cover and the base. Forexample, an epoxy adhesive is applied between each sidewall 204 a of thecover 204 and each corresponding sidewall 202 a of the base 202 to forma hermetic seal between the bent sheet metal cover 204 and the base 202.As described in reference to FIGS. 5A, 5B, the epoxy adhesive may beapplied (e.g., dispensed, or slathered), for example, either all alongthe periphery or at injection points, whereby the dispensed epoxy isautomatically drawn into the seal using capillary action prior to (andpossibly during) curing at an elevated temperature. Furthermore, asdescribed in reference to the tub cover 904 of FIG. 9A, the epoxyadhesive may be dispensed, for example, as a continuous bead around thecomplete perimeter of the sidewall 204 a of the tub cover 204, or thesidewall 202 a of the base 202.

Additional embodiments may include setting a gap between the sidewallsbased on a plurality of protrusions (e.g., protrusions 306 of FIGS. 3A,3B) extending outward from the outer surface of each sidewall of thebase, or setting a gap between the sidewalls based on a plurality ofdimples (e.g., dimples 308 of FIG. 3A) extending inward from the innersurface of each sidewall of the bent sheet metal cover. Additionalembodiments may include inspecting the epoxy adhesive through inspectionholes (e.g., inspection holes 406 of FIG. 4) through each sidewall ofthe gent sheet metal cover.

FIG. 12 is a flowchart illustrating a method for assembling a datastorage device, according to a second embodiment. FIG. 12 is describedwith reference to FIGS. 13A-13C, where FIG. 13A is an exploded viewillustrating a fourth example HDD adhesive seal configuration, FIG. 13Bis a perspective view illustrating a step in the process associated withthe fourth example, and FIG. 13C is a perspective view illustrating ofan assembled HDD from the process associated with the fourth example,according to an embodiment.

At block 1202, a first cover is attached to an enclosure base having aplurality of sidewalls. For example, a conventional HDD cover may beattached to the base with fasteners and with a gasket seal therebetween,whereby servo-writing and manufacturing test may follow.

At block 1204, a flat metal sheet is positioned over the first cover,and at block 1206, the metal sheet is bent over the base to form a bentsheet metal cover comprising a plurality of sidewalls extending at anangle from a top portion such that each sidewall of the bent sheet metalcover overlaps at least in part with a corresponding sidewall of thebase. For example, in FIGS. 13A, 13B a flat, rigid metal sheet 1303 ispositioned over a first cover 1301 (block 1204) and aligned with thebase 1302 using a fixture, for example. Then, the aligned metal sheet1303 is bent (e.g., machine pressed) to form each sidewall 1304 aextending at an angle from the top portion 1304 b such that eachsidewall 1304 a overlaps with a corresponding sidewall 1302 a of base1302 (block 1206), as depicted in FIG. 13C. A fixture may be utilized tohold each sidewall 1304 a at its edge to prevent spring-back. In thiscase, the bent sheet metal cover 1304 is a shape-in-place type of coverbecause the flat metal sheet 1303 is shaped and formed in place over thebase 1302, effectively using the base 1302 as a mold.

At block 1208, a hermetic seal is formed between the bent sheet metalcover 1304 and the base 1302 by applying pressure to apressure-sensitive adhesive (PSA). For example, and according toembodiments, with a PSA-attached cover seal the PSA material (notvisible) may be fixed to the underside of portions of the original flatmetal sheet 1303, or the PSA material may be fixed to top portions ofthe base 1304. PSA has relatively high permeability, therefore theadhesive layer thickness should be limited (e.g., ˜25 μm). On the otherhand, use of PSA can lead to a significantly narrower gap (e.g., ˜25 μm)with less concern for tolerances because the seal thickness is set bythe PSA film thickness rather than by parts tolerances.

An additional embodiment may include, prior to forming the hermeticseal, applying a PSA tape 1305 (shown dashed in FIG. 13C) overlapping abottom edge portion of each sidewall 1304 a of the bent sheet metalcover 1304 and a portion of the corresponding sidewall 1302 a of thebase 1302 adjacent the bottom edge portion of the cover. Use of thinfoil with soft PSA material can ensure that the tape 1305 conforms tothe base and cover, thereby absorbing manufacturing tolerances. A rolleror press with elastic averaging can be used to apply the tape 1305without entrapped bubbles. However, note that a tape seal has two leakpaths (up and down) compared to just one for the case of a PSA-attachedcover seal. Since two leak paths are present, each leak path should bedesigned for a half leak rate, implying that a tape seal should be 4times wider in terms of seal area than a PSA-attached cover seal.Therefore, available height for a tape seal is a consideration.

Tub Cover Corner Configurations

FIG. 14A is a perspective view illustrating a tub cover gathered corner,according to a first embodiment, and FIG. 14B is a perspective viewillustrating a tub cover tapered radius corner, according to a secondembodiment. With the gathered (or “pleated”) corner of FIG. 14A, thistype of tub cover corner has some extra material available by way of thepleat structural configuration. Thus, during an interference fit processeach cover 1404 sidewall 1404 a can deflect outward while pulling someextra material from each corner 1403, thus averting tearing of the covermaterial. However, the gathered material in the corners 1403 couldresult in thick epoxy areas and, consequently, a high leak rate in thecorners 1403. Hence, according to an embodiment, corner horizontal sealsmay be used in such a scenario, such as illustrated and described inreference to FIG. 2.

Tub Cover with Tapered Radius Corners

With the tapered radius corner of FIG. 14B, according to an embodiment,a tub cover 1414 comprises tapered radius corners 1413, in which thecorner radius 1413 a is sharper (smaller) near the bottom edge of thetub cover 1414 (note that the corner 1413 is depicted in an upside downposition) and the corner radius 1413 b is larger near the top of the tubcover 1414.

FIG. 15 is a bottom perspective view illustrating a tub cover havingtapered radius corners, according to an embodiment. Similarly to asillustrated in FIG. 14B, tub cover 1414 (again depicted in an upsidedown position) comprises tapered radius corners in which the bottomcorner radius 1413 a is smaller than the top corner radius 1413 b. Somenon-limiting example dimensions are as follows, where the cover 1414 isdimensioned for a 95 mm form factor HDD, and comprises long sides atabout 146 mm and short sides at about 101 mm. The cover 1414 thicknessmay be about 0.25 mm, with the material being aluminum, for example.Further with this example, the bottom corner radius 1413 a isapproximately 1 mm and the top corner radius 1413 b is approximately4.75 mm. In between the bottom corner radius 1413 a and the top cornerradius 1413 b, the radius gradually changes from 1 mm to 4.75 mm, whichis referred to as a tapered radius (or “lofted”) shape. Still furtherwith this example, the sidewalls 1414 a of cover 1414 is vertical in itsas-formed state (i.e., prior to installing onto a base, such as base1602 of FIGS. 16A, 16B).

Base For Tub Cover with Tapered Radius Corners

FIG. 16A is a top perspective view illustrating an HDD base; FIG. 16B isa cross-sectional perspective view illustrating the base of 16A; andFIG. 16C is a cross-sectional view illustrating a sidewall of the baseof 16A, according to an embodiment. In FIG. 16A, base 1602 comprisescorners 1603 having a constant corner radius matching the top cornerradius 1413 b of a corresponding cover, such as cover 1414 (FIGS. 14B,15). For a non-limiting example, the radius of corners 1603 are aconstant 4.75 mm over the entire height of each sidewall 1602 a thatwill be overlapped by the sidewalls of the cover, such as sidewalls 1414a of cover 1414. With reference to FIG. 16C, note that the top portion1602 a-1 of the outer surface of the sidewall 1602 a is not vertical,but is depicted as sloped at an angle a (e.g., approximately 1.7 degreesfor this example). Both the cover 1414 sidewalls 1414 a and the base1602 sidewalls 1602 a may be sloped, according to an embodiment.However, the base 1602 preferably has more slope than the cover 1414 sothat there is interference between the cover sidewalls 1414 a and basesidewalls 1602 a as the cover 1414 is pushed down onto the sidewalls1602 a of the base 1602.

FIG. 17A is a top perspective view illustrating an HDD assembly having atub cover assembled to a base; FIG. 17B is a cross-sectional side viewillustrating mating sidewalls of the assembly of 17A; and FIG. 17C is across-sectional side view illustrating a corner area of the assembly of17A, illustrating a portion of an assembly process, according to anembodiment. FIGS. 17A-17C illustrates the HDD assembly after the cover1414 has been pushed down over the sidewalls 1602 a of the base 1602.

According to an embodiment, at the top of the base 1602 sidewall 1602 a,the width of the cover 1414 matches the width of the base 1602 (towithin close tolerances), and there is no intentional interferencecreated between the two parts. However, further down the sidewall 1602a, because there is a difference in slopes between the cover 1414sidewall 1414 a (vertical, in the embodiment depicted) and the base 1602sidewall 1602 a (depicted as 1.7 degrees off vertical), there isinterference, as depicted in FIG. 17B. This interference, generallybetween the bottom edge of the sidewall 1414 a and the bottom portion ofthe sloped portion of the sidewall 1602 a (see, e.g., angle a of FIG.16C), forces the sidewalls 1414 a of the cover 1414 outward (i.e., thecover is thin and relatively weak, while the base is thick andrelatively strong), thereby causing or resulting in an inward forceexerted by the sidewalls 1414 a against the sidewalls 1602 a of the base1602. Hence, the hermetic seal formed between the cover 1414 and thebase 1602 is based on this inward force, since the epoxy seal is appliedbetween the two respective sidewalls 1414 a, 1602 a and the inward forcecompresses the liquid epoxy to form a very thin (and thus hermetic)adhesive bond.

However, as the sidewalls 1414 a of the cover 1414 are forced outward bythe slope on the sidewalls 1602 a of the base 1602, “extra” material isneeded to provide for this apparent increase in perimeter. Such “extra”material is effectively available in the corners 1413 of the cover 1414,because of the tapered radius (1413 a relative to 1413 b) of the corners1413 a. That is, if the cover had a constant corner radius (e.g., 4.75mm), the cover corners would fit tightly over the base corner radius(e.g., 4.75 mm). However, since the corner radius 1413 of the cover 1414gradually decreases (for a non-limiting example, from a top radius 1413b of 4.75 mm at the top of the cover corner 1413 to a bottom radius 1413a of 1 mm at the bottom of the cover corner 1413), there is some extramaterial in the corners 1413. Thus, as the cover 1414 sidewalls 1414 aare pushed outward (as depicted by the arrow in FIG. 17B) by pushing thecover 1414 onto the sloped base 1602 sidewalls 1602 a, the extramaterial in the cover corners 1413 is pulled inward (as depicted by thearrow in FIG. 17C) and toward the sidewalls 1602 a. This provision ofextra material in the corners 1413 of the tub cover 1414 provides forlower stresses and avoids tearing of the cover 1414 material at thecorners 1413.

If fabrication tolerances are well controlled, the final state of theinstalled cover 1414 should have the cover sidewalls 1414 a biasedagainst the base 1602, with minimal excess material remaining in thecorners 1413. Such corners 1413 may not necessarily form a very narrowbond line, so the leak rate in the corners 1413 could be higher thanalong the sidewalls 1414 a. However, since the corners 1413 only occupya small fraction of the total perimeter seal, a somewhat higher leakrate per unit length at the corners 1413 can be tolerated while keepingthe entire cover seal within a specified leak budget.

Method of Assembling a Data Storage Device with a Tub Cover andPerimeter Adhesive Seal

With HDD configurations in which a tub cover is used (e.g., in lieu of abent metal sheet cover), a similar process to the process described inreference to FIG. 11 may be used to assemble a tub cover-basedhermetically-sealed HDD. Therefore, reference is made to FIG. 11 for oneapproach to assembling a tub cover with an HDD base, according to anembodiment, where the use of a tub cover is substituted for a bent metalsheet cover.

FIG. 18 is a flow diagram illustrating a method of assembling a datastorage device, according to an embodiment.

At block 1802, a first cover is attached to an enclosure base having aplurality of sidewalls interposed between corners each having asubstantially constant-radius outer surface. For example, a conventionalHDD cover may be attached to a base 1602 with fasteners and with agasket seal therebetween, where the base 1602 comprises constant-radiuscorners, and whereby servo-writing and manufacturing test may follow.

At block 1804, each of a plurality of sidewalls of a tub cover ispositioned to overlap at least in part with a corresponding sidewall ofthe base, wherein each of a plurality of corners of the tub cover has atapered radius that decreases from a top portion of the tub cover in thedirection of the bottom edge of the tub cover. Further, the positioningincludes forming an interference fit between the base and the tub coverat areas where the corners of the base and tub cover mate, by forcingoutward each sidewall of the tub cover while forcing inward at least aportion of each corner of the tub cover. For example, each sidewall 1414a (FIGS. 15, 17) of the cover 1414 (FIGS. 15, 17) is positioned tooverlap with a portion of a corresponding sidewall 1602 a (FIGS. 16A-C,17) of the base 1602 (FIGS. 16A, 16B, 17), where each corner 1413 (FIGS.14B, 15, 17) of the cover 1414 has a tapered radius, such as describedand illustrated by bottom corner radius 1413 a (FIGS. 14B, 15, 17) andtop corner radius 1413 b (FIGS. 14B, 15, 17). Further, with thepositioning of block 1804, an interference fit is formed between thebase 1602 and the tub cover 1414, by forcing outward each sidewall 1414a of the tub cover (e.g., arrow of FIG. 17B) while forcing inward atleast a portion of each corner 1413 of the tub cover (e.g., arrow ofFIG. 17C). With suitable flexibility associated with the tub cover, theinward deflection of the corners may occur simply as a result of theoutward deflection of the sidewalls caused by the interference betweenthe parts during assembly.

At block 1806, an epoxy adhesive is applied at an interface of eachsidewall of the tub cover and each corresponding sidewall of the base toform a hermetic seal between (or among) the tub cover and the base. Forexample, an epoxy adhesive is applied between each sidewall 1414 a(FIGS. 15, 17) of the cover 1414 (FIGS. 15, 17) and each correspondingsidewall 1602 a (FIGS. 16A-C, 17) of the base 1602 (FIGS. 16A, 16B, 17)to form a hermetic seal between the tub cover 1414 and the base 1602. Asdescribed in reference to FIGS. 5A, 5B, a liquid epoxy adhesive may beapplied, for example, either all along the periphery or at injectionpoints, whereby the dispensed epoxy is automatically drawn into the sealusing capillary action, after assembly and prior to curing at anelevated temperature. Furthermore, as described in reference to the tubcover 904 of FIG. 9A, the epoxy adhesive may be dispensed, for example,as a continuous bead around the complete inside perimeter of thesidewall 1414 a of the tub cover 1414, or the outside perimeter sidewall1602 a of the base 1602, or both, prior to assembly. Still further, anepoxy adhesive could be applied at or near where the bottom edge of thesidewall 1414 a of the tub cover 1414 meets with the base 1602, ratherthan precisely “between” the two parts.

Note that the adhesive sealant does not have to be epoxy, as otherpolymeric adhesives may be used. Furthermore, a heat-sealing materialmay be used by applying the material to one of the mating parts, andthen heating the cover and base assembly after assembly to reflow theheat-seal material. Soldering may also be an option.

Method of Assembling a Data Storage Device with Perimeter Adhesive Seal

FIG. 19 is a flow diagram illustrating a method of assembling a datastorage device, according to an embodiment.

At block 1902, an enclosure is formed by positioning each of a pluralityof sidewalls extending from a top portion of a cover to overlap at leastin part with a corresponding sidewall of a base part. For example, forman enclosure by positioning the sidewalls of the cover 604 (FIG. 6C) tooverlap with the sidewalls of the base 602 (FIGS. 6B, 6C).

At block 1904, a liquid adhesive is dispensed between each sidewall ofthe cover and the corresponding sidewall of the base part, in such aquantity at each of a plurality of locations, to promote capillary flowof the liquid adhesive to form a continuous film of the liquid adhesivebetween the sidewalls around the entire perimeter of the enclosure. Forexample, a liquid adhesive (e.g., a liquid epoxy) is dispensed betweenthe respective sidewalls of the cover 604 and the base 602, via theplurality of filling features 606 (FIGS. 6A-8), in a manner suitable forpromoting the desired capillary flow in order to form the desiredcontinuous film of liquid adhesive (e.g., between the sidewalls of thecover 604 and the base 602 around the entire perimeter of the HDDassembly 600 (FIG. 6C). Recall that an adhesive seal/bond line thicknessof around 0.1 mm and a width (or height) of around 5-10 mm or more isconsidered suitable.

In this context, a “substantially” continuous film of liquid adhesivemay be sufficient, where minute discontinuities in the adhesive could bepresent while the effectiveness of the seal still falls within thedesired leak budget.

At block 1906, the continuous film of liquid adhesive is cured, to forma hermetic seal between the cover and the base part. According toembodiments, the surface treatment and gap control techniques describedelsewhere herein, for example, may be applied to this assembly methodfor enhancing the capillary flow and controlling the seal thickness(i.e., by controlling the gap), respectively.

Extensions and Alternatives

Implementation and use of embodiments described herein are not limitedsolely to individual HDDs. Rather, embodiments involving the use ofparticular cover and base configurations/geometries to provide asufficiently low-permeable cover-to-base perimeter seal, may also beapplied to a system level sealed tray or box of multiple HDDs enclosedin a box containing gas like He or N₂, as well as to hermetically-sealedelectronic devices, generally (e.g., optical systems, optical datastorage devices, and the like).

In the foregoing description, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Therefore, various modifications andchanges may be made thereto without departing from the broader spiritand scope of the embodiments. Thus, the sole and exclusive indicator ofwhat is the invention, and is intended by the applicants to be theinvention, is the set of claims that issue from this application, in thespecific form in which such claims issue, including any subsequentcorrection. Any definitions expressly set forth herein for termscontained in such claims shall govern the meaning of such terms as usedin the claims. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

In addition, in this description certain process steps may be set forthin a particular order, and alphabetic and alphanumeric labels may beused to identify certain steps. Unless specifically stated in thedescription, embodiments are not necessarily limited to any particularorder of carrying out such steps. In particular, the labels are usedmerely for convenient identification of steps, and are not intended tospecify or require a particular order of carrying out such steps.

What is claimed is:
 1. A data storage device comprising: an enclosurebase comprising a plurality of sidewalls and corner portions; a tubcover comprising continuous sidewalls extending from a top portion andincluding corner portions, wherein each said sidewall and said cornerportion of said tub cover overlaps at least in part with a correspondingsaid sidewall and a corresponding said corner portion of said base,wherein each said corner portion of said tub cover comprises a pleatedcorner; and a hermetic seal among said base and said tub cover,comprising: an epoxy adhesive at: an interface of each said sidewall ofsaid tub cover and each said corresponding sidewall of said base, and aninterface of each said corner portion of said tub cover and each saidcorresponding corner portion of said base.
 2. The data storage device ofclaim 1, wherein each said sidewall of said base has an outer surfaceand each said sidewall of said tub cover has an inner surface, andwherein said base comprises a plurality of protrusions extending outwardfrom said outer surface of each said sidewall and positioned to set aparticular gap between said inner surface and said outer surface.
 3. Thedata storage device of claim 1, wherein each said sidewall of said basehas an outer surface and each said sidewall of said tub cover has aninner surface, and wherein said tub cover comprises a plurality ofdimples extending a distance inward from said inner surface of each saidsidewall and positioned to set a particular gap between said innersurface and said outer surface.
 4. The data storage device of claim 1,wherein each said sidewall of said base has an outer surface and eachsaid sidewall of said tub cover has an inner surface, and wherein atleast one of said outer and inner surfaces is an abrasive blasted,chemical etched, feature formed, and cut feature formed surface.
 5. Thedata storage device of claim 1, wherein said tub cover comprises one ormore inspection holes through each said sidewall.
 6. The data storagedevice of claim 1, wherein each said sidewall of said tub cover extendsfrom said top portion at an angle greater than 90 degrees.
 7. The datastorage device of claim 1, wherein at least one said sidewall of saidbase comprises a chamfer at its top.
 8. The data storage device of claim1, wherein said base comprises a plurality of adhesive filling slotsspaced around its perimeter.
 9. The data storage device of claim 1,wherein each said sidewall of said tub cover comprises a sloped sectionfollowed by a substantially vertical alignment skirt extending in thedirection of a bottom edge, and wherein each said sidewall of said basecomprises a chamfer, and wherein said hermetic seal is positioned in anadhesive area where said sloped section of said tub cover and saidchamfer of said base mate.
 10. The data storage device of claim 9,wherein said epoxy adhesive is applied to said sloped section of eachsaid sidewall and to each said corner portion of said tub cover as asubstantially continuous epoxy bead.
 11. The data storage device ofclaim 1, wherein each said sidewall of said tub cover is substantiallyvertical along a majority of its length.
 12. The data storage device ofclaim 11, wherein each said sidewall of said base comprises an inwardlysloped upper portion corresponding to an area at which each saidsidewall of said tub cover overlaps.
 13. The data storage device ofclaim 1, wherein each said sidewall of said tub cover is outwardlysloped at a first angle; wherein each said sidewall of said basecomprises an upper portion that is inwardly sloped at a second angle;wherein said first angle is less than said second angle, such that aninterference fit occurs between a bottom edge of said tub cover and abottom portion of said upper portion of said base.
 14. A method ofassembling a data storage device, the method comprising: providing anenclosure base comprising a plurality of sidewalls, wherein each saidsidewall of said base is interposed between two corner portions;positioning each of a plurality of continuous sidewalls extending from atop portion of a tub cover and each of a plurality of corner portions ofsaid tub cover to overlap at least in part with a corresponding saidsidewall and corresponding said corner portion of said base, whereineach of the plurality of corner portions of said tub cover comprises apleated corner, wherein said positioning includes forming aninterference fit between said base and said tub cover where said cornerportions of said base and said tub cover mate; and applying an epoxyadhesive at an interface of each said sidewall and each said cornerportion of said tub cover and each said corresponding sidewall and eachsaid corresponding corner portion of said base to form a hermetic sealamong said tub cover and said base.
 15. The method of claim 14, whereinpositioning includes setting a gap, based on a plurality of protrusionsextending outward from an outer surface of each said sidewall of saidbase, between each said sidewall of said tub cover and saidcorresponding sidewall of said base.
 16. The method of claim 14, whereinpositioning includes setting a gap, based on a plurality of dimplesextending inward from an inner surface of each said sidewall of said tubcover, between each said sidewall of said tub cover and saidcorresponding sidewall of said base.
 17. The method of claim 14, furthercomprising: prior to applying said epoxy adhesive, treating at least oneinner surface of said tub cover or one outer surface of said base usingone or more surface treatment techniques from a group consisting ofabrasive blasting, chemical etching, feature forming, and cut featureforming.
 18. The method of claim 14, further comprising: inspecting saidepoxy adhesive through one or more inspection holes through each saidsidewall of said tub cover.
 19. The method of claim 14, wherein saidbase comprises a plurality of adhesive filling slots spaced around itsperimeter, and wherein applying said epoxy adhesive includes applying aliquid epoxy via said plurality of adhesive filling slots.
 20. Themethod of claim 14, wherein each said sidewall of said tub covercomprises a sloped section followed by a substantially verticalalignment skirt extending in a direction of a bottom edge, and whereineach said sidewall of said base comprises a chamfer at its top, andwherein applying includes, prior to said positioning, applying saidepoxy adhesive to said sloped section of each said sidewall and to eachcorner of said tub cover as a substantially continuous epoxy bead suchthat said hermetic seal is positioned where said sloped section of saidtub cover and said chamfer of said base mate.
 21. The method of claim14, wherein each said sidewall of said tub cover is outwardly sloped ata first angle, and wherein each said sidewall of said base comprises anupper portion that is inwardly sloped at a second angle, and whereinsaid first angle is less than said second angle, and wherein formingsaid interference fit includes creating interference between a bottomedge of said tub cover and a bottom portion of said upper portion ofsaid base.